CVE-2026-5947

SIG(0) validation during query flood may lead to undefined behavior

State: Published
Severity: 7.5 High
Published: May 20, 2026
Updated: Sep 1, 2026
Reserved: Apr 9, 2026

Description

Undefined behavior may result due to a race condition leading to a use-after-free violation. If BIND receives an incoming DNS message signed with SIG(0), it begins work to validate that signature. If, during that validation, the "recursive-clients" limit is reached (as would occur during a query flood), and that same DNS message is discarded per the limit, there is a brief window of time while the SIG(0) validation may attempt to read the now-discarded DNS message. This issue affects BIND 9 versions 9.20.0 through 9.20.22, 9.21.0 through 9.21.21, and 9.20.9-S1 through 9.20.22-S1. BIND 9 versions 9.18.28 through 9.18.49 and 9.18.28-S1 through 9.18.49-S1 are NOT affected.

Scores

CVSS	Score	Vector	Source
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	isc
3.1	7.5 High	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H	redhat-SADP

Weaknesses

CWE-362 Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-416 Use After Free
CWE-367 Time-of-check Time-of-use (TOCTOU) Race Condition

Affected Products

Product	Versions
BIND 9ISC	9.20.0 through 9.20.22Affected 9.21.0 through 9.21.21Affected 9.20.9-S1 through 9.20.22-S1Affected 9.18.28 through 9.18.49Not affected 9.18.28-S1 through 9.18.49-S1Not affected

References

CVE-2026-5947vendor-advisory
https://downloads.isc.org/isc/bind9/9.20.23patch
https://downloads.isc.org/isc/bind9/9.21.22patch
https://access.redhat.com/security/cve/CVE-2026-5947vdb-entry
RHBZ#2479772issue-tracking
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-5947.json
https://access.redhat.com/errata/RHSA-2026:7412vendor-advisory

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